(391d) Energy Efficient Approach for Direct Air Capture

Accomplishing the Department of Energy’s goal of capturing CO₂ from the air for less than $100/metric ton of CO₂ equivalents warrants an urgent development of energy-efficient capture technologies. Out of the technologies available for CO₂ capture, water-driven CO₂ capture is attractive because they incur a low energy penalty. The Migration Assisted Moisture Gradient (MAMG) process captures and regenerates CO₂ based on the bicarbonate-carbonate equilibria. The CO₂ capture occurs in an organic phase and captured CO₂ migrates to the aqueous phase separated by the membrane under an external bias. Ionic Liquids (ILs) can improve the energy efficiency of the process due to their low vapor pressure and high conductivities achieved by hydrogen bonding. Herein we present the results of improving the energy efficiency of the MAMG process by studying the effects of various ILs. Moreover, we also demonstrate the results from the large-scale operation of the MAMG process in a Bipolar Membrane Electro Dialysis unit (BPMED) unit for CO₂ capture from air. The BPMED consists of alternating layers of BPM and AEM separating the aqueous and the organic medium. The water-splitting reaction at the interface of the BPM additionally maintains electroneutrality throughout the organic and aqueous phases. Parameters such as the surface area of the membrane, effects of IL concentration, varying composition of CO₂, impurities such as SO_x, and relative humidity of the air on the rate of CO₂ capture will also be presented.